Seminar

3-D Evolution of the Crustal Magnetic Field in Neutron Stars

Speaker:Konstantinos Gourgouliatos, U Leeds

Date:December 10, 2015

Time:4:15 pm

Location:Pupin 1402

Host:Brian Metzger

The evolution of the crustal magnetic field in neutron stars is mediated by
two processes: Hall drift and Ohmic dissipation. Hall drift is the
advection of the magnetic field lines by freely moving electrons in the
rigid crust and dominates the evolution for magnetic fields above 10^13 G.
While the Hall effect conserves energy, it has been suggested that it can
accelerate Ohmic dissipation; however axially symmetric calculations so far
have found only a modest increase in the decay rate when the Hall effect is
included, compared to pure Ohmic dissipation. We find that, unlike the
axially symmetric calculations, the magnetic field evolution in 3-D is
susceptible to instabilities, provided that ~50% of the magnetic field
energy is in the toroidal component of the field. These instabilities
severely deform the large-scale structure of the field and lead to the
formation of kilometer-sized structures where the magnetic field intensity
is an order of magnitude higher than the spin-down dipole field. These
localised magnetic fields are sites of efficient dissipation generating
heat. Furthermore, the strong Maxwell stresses developed can trigger
magnetar activity. Thus, we suggest that the Hall effect is capable of
rearranging the magnetic field in a neutron star crust creating "magnetic
spots" where the intensity is above 10^15 G while the dipole field is
~10^14. This makes magnetar theory more economical as it removes the need
for extremely strong concealed magnetic fields while it provides a natural
mechanism for the creation of hotspots suggested by observations .